The present invention relates to a method of cutting an inside corner of a workpiece and a cutting tool for cutting the inside corner.
In order to cut the inside corner of the workpiece, for example, an inside corner of a workpiece pocket, such as a die hole in a mold, there is generally used a rotating cutting tool (e.g. columnar end mill) in the machining or a rod electrode, a wire electrode, etc. in the electrical discharge machining.
In cutting the pocket by the end mill, it is impossible to carry out the processing (processing of corner R) of an inside corner having a curvature radius smaller than a radius of the tool and therefore, the end mill is required to have a radius less than the minimum radius of curvature of the inside corner. Additionally, if the pocket is deep, then it requires a long tool having a small diameter, accompanying the possibility of inappropriate cutting because of insufficient rigidity of the tool itself. Further in the end milling, it is impossible to process an inside corner having an acute angle (e.g. 90 degrees) called xe2x80x9cpin anglexe2x80x9d.
Therefore, when processing the inside corner so as to have a small radius of curvature and the pocket to be large in depth or processing the above pin corner, the electrical discharge machining has been generally allocated rather than the cutting using the cutting tool. However, the electrical discharge machining has a drawback of inefficient workability in comparison with the machining efficiency of cutting, causing the machining cost to be increased. Under such a situation, there is a great demand to make the electrical discharge machining unnecessary in view of shortening the machining lead time, whereby all the processing is completed by a single machine tool.
It is therefore an object of the present invention to provide an inside corner cutting method where the above-mentioned working (i.e. formation of an inside corner having a small curvature radius and a pocket having a large depth; formation of an inside corner having an acute angle, such as 90 degrees, called xe2x80x9cpin anglexe2x80x9d) can be effectively completed by the cutting and further provide a cutting tool for embodying the inside corner cutting method.
In order to accomplish the above object, the present invention provides the inside corner cutting method characterized by the following features. First, a cutting tool used in the method has at least one cutting edge formed at its bottom part and is driven to rotate. The cutting tool and the workpiece to be processed move relatively to each other in accordance with the rotating angle of the cutting tool so that the cutting tool has its outer end describing a moving track in agreement with the contour of the inside corner of the workpiece as the object to be processed. Further, the cutting tool moves along the direction of a rotating axis of the rotating cutting tool. Note that, in this specification, the rotating axis of the cutting tool is identical to its longitudinal axis passing through a rotating center of the cutting tool.
According to the above method, repeatedly, the cutting tool having the cutting edge is used. The so-rotated cutting tool and the workpiece to be processed relatively move in a manner that an outer end of the cutting edge describes the moving track in agreement with the contour of the inside corner of the workpiece, while the cutting tool is also displaced along the direction of the rotating axis of the rotating cutting tool. Accordingly, while maintaining the rigidity of the tool sufficiently, the above-mentioned working (i.e. formation of an inside corner having a small curvature radius and a pocket having a large depth; formation of an inside corner having an acute angle, such as 90 degrees, called xe2x80x9cpin anglexe2x80x9d) can be effectively completed by the only cutting.
The cutting tool and the workpiece may move relatively to each other in a plane crossing the rotating axis of the cutting tool. Further, the relative movement between the cutting tool and the workpiece is fixed and unchangeable throughout the whole movement of the cutting tool in the direction of the rotating axis.
In the above-mentioned method, it is executed to cut the inside corner under condition that the relative movement in the plane crossing the rotating axis is fixed and unchangeable throughout the whole movement of the cutting tool in the direction of the rotating axis. Thus, the R(round) processing and the xe2x80x9cpin anglexe2x80x9d processing can be accomplished against the inside corner succeeding to vertical faces (i.e. surfaces parallel to the rotating axis of the tool) by the only cutting, efficiently.
Alternatively, the relative movement between the cutting tool and the workpiece may change corresponding to the movement of the cutting tool in the direction of the rotating axis.
In this case, it is executed to cut the inside corner under condition that the relative movement in the plane crossing the rotating axis changes corresponding to the movement of the cutting tool in the direction of the rotating axis. Thus, the R(round) processing and the xe2x80x9cpin anglexe2x80x9d processing can be accomplished against the inside corner succeeding to inclined faces (i.e. surfaces inclined to the rotating axis of the tool) by the only cutting, efficiently.
In the above-mentioned method, there may be employed a cutting tool which includes a main body detachably attached to a main spindle of the machine tool so as to rotate about the rotating axis of the cutting tool in rotation and a cutting edge arranged on a straight line deviated from the rotating axis and also fixed on a bottom face of the main body. Owing to the adoption of the cutting tool, the above method.could be embodied efficiently.
Apropos of this cutting tool, the bottom face of the main body may be substantially configured in the form of a polygon in plan view. Further, the cutting edge may be arranged on one side of the polygon so as to extend from one peak of the polygon toward another peak thereof and the cutting edge may have a length generally equal to half of the one side of the polygon. The bottom face of the main body may be provided, behind the cutting edge in the rotating direction of the cutting tool, with a xe2x80x9crun offxe2x80x9d angle. Owing to the adoption of the cutting tool, the above method could be embodied more efficiently.